One of the critical challenges in engineering is the wireless transfer of energy to power miniaturized electronic devices that have sizes smaller than the wavelength of electromagnetic radiation. Here, we describe a strategy to self-fold three-dimensional (3D) low gigahertz responsive antennas with small form factors using capillary forces. The antennas are sub-millimeter (500 × 500 × 500 (m3) cubic devices with small form factors and hollow free space in their interior which could be used to embed other devices. We characterize and demonstrate the efficacy of these antennas in dispersive media. Remarkeably, we observe significantly higher power transfer with over an order of magnitude higher transfer efficiency as compared to similarly shaped planar antennas. Moreover, we show that the antennas can transfer on the order of 30 mW to power an LED, highlighting proof of concept for practical applications. Our findings suggest that self-folding polyhedral microantennas could provide a viable solution for powering tiny microdevices.

A new approach to fabricate copper, indium, gallium diselenide (CIGSe) solar cells on conductive fluorinedoped tin oxide (FTO) reached an efficiency of over 6% for a champion photovoltaic device. Commercial oxide nanoparticles are formulated into high-quality screen-printable ink based on ethyl cellulose solution in terpineol. The high homogeneity and good adhesion properties of the oxide ink play an important role in obtaining dense and highly crystalline photoabsorber layers. This finding reveals that solution-based screen-printing from readily available oxide precursors provides an interesting cost-effective alternative to current vacuum-and energy-demanding processes of the CIGSe solar cell fabrication.

This paper reports a 3D small micro-antenna suitable for energy harvesting applications in the low gigahertz regime to supply 1μW power to small, implantable medical device. The micro antenna is designed to envelope a 500 × 500 × 500 μm 3 implantable device and simulated as embedded in 5 × 5 × 5 mm 3 of muscle tissue. The proposed antenna was fabricated by combining planar photolithography and surface tension driven self-folding techniques in order to achieve the desired 3D profile.

Objective. As electrodes are required to interact with sub-millimeter neural structures, innovative microfabrication processes are required to enable fabrication of microdevices involved in such stimulation and/or recording. This requires the development of highly integrated and miniaturized systems, comprising die-integration-compatible technology and flexible microelectrodes. To elicit selective stimulation and recordings of sub-neural structures, such microfabrication process flow can beneficiate from the integration of titanium nitride (TiN) microelectrodes onto a polyimide substrate. Finally, assembling onto cuffs is required, as well as electrode characterization. Approach. Flexible TiN microelectrode array integration and miniaturization was achieved through microfabrication technology based on microelectromechanical systems (MEMS) and complementary metal-oxide semiconductor processing techniques and materials. They are highly reproducible processes, granting extreme control over the feature size and shape, as well as enabling the integration of on-chip electronics. This design is intended to enhance the integration of future electronic modules, with high gains on device miniaturization. Main results. (a) Fabrication of two electrode designs, (1) 2 mm long array with 14 TiN square-shaped microelectrodes (80 × 80 µm 2 ), and (2) an electrode array with 2 mm × 80 µm contacts. The average impedances at 1 kHz were 59 and 5.5 kΩ, respectively, for the smaller and larger contacts. Both designs were patterned on a flexible substrate and directly interconnected with a silicon chip. (b) Integration of flexible microelectrode array onto a cuff electrode designed for acute stimulation of the sub-millimeter nerves. (c) The TiN electrodes exhibited capacitive charge transfer, a water window of −0.6 V to 0.8 V, and a maximum charge injection capacity of 154 ± 16 µC cm −2 . Significance. We present the concept, fabrication and characterization of composite and flexible cuff electrodes, compatible with post-processing and MEMS packaging technologies, which allow for compact integration with control, readout and RF electronics. The fabricated TiN microelectrodes were electrochemically characterized and exhibited a comparable performance to other state-of-the-art electrodes for neural stimulation and recording. Therefore, the presented TiN-on-polyimide microelectrodes, released from silicon wafers, are a promising solution for neural interfaces targeted at sub-millimeter nerves, which may benefit from future upgrades with die-electronic modules.

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